1. Field of the Invention
This invention concerns corrosion detection in general. More specifically, it deals with an improved combination of a corrosion detection probe and a temperature control. The combination provides an ability to obtain maximum corrosive conditions at the location of a corrosion probe.
2. Description of the Prior Art
Different types of instruments have heretofore been used to measure the corrosion rate of various metals. Some of these instruments make use of electrochemical properties of the metal in an electrically conductive corrosive. Other instruments employ different testing techniques that measure electrochemical properties to monitor the corrosion rates. These latter are generally referred to as polarization, galvanic couples, and corrosion potential methods. Other instruments measure corrosion rate by monitoring the increase of electrical resistance of an exposed sample, or measuring element.
All of the foregoing techniques use corrosion probes that expose one or more metal coupons, or test specimens to the corrosive medium being studied (or measured). Such coupons are connected in an electric circuit so that either the electrochemical properties or the change in electrical resistance can be observed and employed to determine the rate of corrosion. However, it has been found that incorrect positioning of the probe or probes with regard to the local corrosive conditions in various types of equipment has led to misleading and incorrect corrosion rate measurement.
One prior attempt to eliminate such inaccuracies has been to employ a flush mounted electrode structure. For example, see that described in the U.S. Pat. No. 3,948,744, to R. H. Cushing, issued Apr. 6, 1976. Still, probe location has remained a very serious problem. Thus, in processes where temperature and pressure conditions are such that condensation or evaporation of corrosive is possible in certain regions of the process, the corrosion will tend to be localized in such regions. Furthermore, since the locations of these regions are generally not predictable, a corrosion probe may very likely not be located at such a region and consequently it would miss the corrosion phenomenon.
Because the foregoing conditions have existed, it has been found that failures may occur with catastrophic results, while the corrosion rate measurement being affected had not indicated any danger. Thus, small amounts of condensed water accumulating acid components has caused severe localized corrosion in the upper parts of a distillation column and an overhead system of a petroleum type plant. Also, in many other process operations in the petroleum industry, severe corrosion problems may be met when handling vapors near dew point temperatures. Therefore, effective control of corrosion in such cases can only be realized by use of corrosion probes which create regions with temperatures at which condensation or evaporation may occur.
Consequently, it is an object of this invention to provide means for controlling the temperature of a measuring element (or coupon), compared to that of the surrounding metal of a corrosion probe. Also, the means may include probe temperature measurement and remote electrical operation.
Another object of the invention is to teach a method of making corrosion measurements. It comprises the steps of locating a probe within a container having a corrosive atmosphere therein, and regulating the temperature of a measuring element of the probe to produce maximum corrosive conditions at that location.